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rcu-tasks: Report stalls during synchronize_srcu() in rcu_tasks_postscan()

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The call to synchronize_srcu() from rcu_tasks_postscan() can be stalled
by a task getting stuck in do_exit() between that function's calls to
exit_tasks_rcu_start() and exit_tasks_rcu_finish().   To ease diagnosis
of this situation, print a stall warning message every rcu_task_stall_info
period when rcu_tasks_postscan() is stalled.

[ paulmck: Adjust to handle CONFIG_SMP=n. ]

Acked-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reported-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/rcu/20230111212736.GA1062057@paulmck-ThinkPad-P17-Gen-1/
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
This commit is contained in:
Neeraj Upadhyay
2023-01-11 13:15:00 +05:30
committed by Joel Fernandes (Google)
parent 7ea91307ad
commit a4533cc0a5
1 changed files with 31 additions and 0 deletions
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31
kernel/rcu/tasks.h
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@@ -139,6 +139,12 @@ static struct rcu_tasks rt_name = \
/* Track exiting tasks in order to allow them to be waited for. */
DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
#ifdef CONFIG_TASKS_RCU
/* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */
static void tasks_rcu_exit_srcu_stall(struct timer_list *unused);
static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall);
#endif
/* Avoid IPIing CPUs early in the grace period. */
#define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0)
static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY;
@@ -830,6 +836,13 @@ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
/* Processing between scanning taskslist and draining the holdout list. */
static void rcu_tasks_postscan(struct list_head *hop)
{
int rtsi = READ_ONCE(rcu_task_stall_info);
if (!IS_ENABLED(CONFIG_TINY_RCU)) {
tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi;
add_timer(&tasks_rcu_exit_srcu_stall_timer);
}
/*
* Exiting tasks may escape the tasklist scan. Those are vulnerable
* until their final schedule() with TASK_DEAD state. To cope with
@@ -848,6 +861,9 @@ static void rcu_tasks_postscan(struct list_head *hop)
* call to synchronize_rcu().
*/
synchronize_srcu(&tasks_rcu_exit_srcu);
if (!IS_ENABLED(CONFIG_TINY_RCU))
del_timer_sync(&tasks_rcu_exit_srcu_stall_timer);
}
/* See if tasks are still holding out, complain if so. */
@@ -923,6 +939,21 @@ static void rcu_tasks_postgp(struct rcu_tasks *rtp)
void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");
static void tasks_rcu_exit_srcu_stall(struct timer_list *unused)
{
#ifndef CONFIG_TINY_RCU
int rtsi;
rtsi = READ_ONCE(rcu_task_stall_info);
pr_info("%s: %s grace period number %lu (since boot) gp_state: %s is %lu jiffies old.\n",
__func__, rcu_tasks.kname, rcu_tasks.tasks_gp_seq,
tasks_gp_state_getname(&rcu_tasks), jiffies - rcu_tasks.gp_jiffies);
pr_info("Please check any exiting tasks stuck between calls to exit_tasks_rcu_start() and exit_tasks_rcu_finish()\n");
tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi;
add_timer(&tasks_rcu_exit_srcu_stall_timer);
#endif // #ifndef CONFIG_TINY_RCU
}
/**
* call_rcu_tasks() - Queue an RCU for invocation task-based grace period
* @rhp: structure to be used for queueing the RCU updates.